Broccoli (Brassica oleracea L. var. italica) has become an increasingly popular crop worldwide especially in health-conscious areas of the western world such as the North America, Europe, and Japan. An average broccoli stalk contains only 30 calories and provides 240% of the recommended daily allowance of vitamin C plus 10% of the recommended daily allowance of vitamin A. In addition to its nutritional value, some recent studies have shown that broccoli aids in the prevention of some forms of cancer.
Broccoli is a cool weather crop. High temperatures (&gt;80.degree. F.) for even relatively short periods of time and warm temperatures (&gt;75.degree. F.) for extended periods of time cause broccoli heads to be rough with uneven flower bud sizes and thus commercially unacceptable. (Bjorkman, T., et al. (1998) High temperature arrest of inflorescence development in broccoli (Brassica oleracea var. italica L.). Journal of Experimental Botany 49:101-106. As a result of the high sensitivity to heat during growth, broccoli can only be grown in limited areas under cool weather conditions.
Previous attempts at identifying heat tolerant broccoli cultivars have not been successful because broccoli is sensitive to relatively short periods of heat stress thereby making field observations too variable for effective genetic screening. Bjorkman, et al. (1998).
Thus, there is a need to develop heat tolerant broccoli varieties that will produce commercially acceptable broccoli heads under warm weather heat stress growth conditions. In addition, there is a need to develop heat tolerant broccoli inbred lines useful for producing heat tolerant F1 seed.